Various aspects of collagen metabolism will be examined both biochemically and histochemically in two animal models of pulmonary fibrosis. Wistar rats and chronic respiratory-disease-free (CRDF) rats of the Sprague-Dawley strain will receive a single intratracheal instillation of silica dust. These rats, and control populations, will be examined at intervals up to one year after exposure. Wistar rats have been shown by others to develop "classic" silicosis, closely resembling the human disease, within one year after this type of exposure to silica. CRDF rats, on the other hand, manifest an atypical silicosis consisting of alveolar proteinosis, which in some respects resembles human acute silicosis. Biochemical studies will include quantitation of collagen synthesis rate, quantitation of Type I/Type III collagen ratios of newly synthesized collagen, quantitation of total lung hydroxyproline, and quantitation of total (unlabelled) Type I/Type III collagen ratios. Newly synthesized collagen will be analyzed by labelling with the radioactive precursor of hydroxyproline, 3(H) proline, in a lung explant system. In addition to these biochemical studies, histochemical evaluation of representative lung sections, using special connective tissue stains (Masson's Trichrome and silver impregnation by the method of Gomori), will be done at the same time points.